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Title |
Calculation of Crack Width of the Top Flange of PSC Box Girder Bridge Considering Restraint Drying Shrinkage
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Authors |
구영호(Young-Ho Ku) ; 한상묵(Sang-Mook Han) |
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DOI |
https://doi.org/10.11112/jksmi.2023.27.3.30 |
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Keywords |
PSCB 거더교; 상부플랜지; 하부플랜지; 구속 건조수축; 균열; 간접하중 PSCB girder bridge; Top flange; Bottom flange; Restraint drying shrinkage; Crack; Indirect load |
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Abstract |
The PSCB girder bridge is a closed cross-section in which the top and bottom flanges and the web are integrated, and the structural characteristics are generally different from the bridges in which the girder and the floor plate are separated, so a maintenance plan that reflects the characteristics of the PSCB girder bridge is required. As a result of analyzing damage types by collecting detailed safety diagnosis reports of highway PSCB girder bridges, most of the deterioration and damage occurring during use is concentrated on the top flange. In particular, cracks in the bridge direction on the underside of the top flange occurred in about 70 % of the PSCB girder bridges to be analyzed, and these cracks were judged to be caused by indirect loads such as heat of hydration and drying shrinkage rather than structural cracks caused by external loads. In order to improve durability and reduce maintenance costs of PSCB girder bridges in use, it is necessary to control restraint drying shrinkage cracks from the design stage. Therefore, in this paper, the cracks caused by drying shrinkage under restraint, which is the main cause of cracks under the flanges of the top part of the PSCB girder bridge, were directly calculated using the Gilbert Model, and the influencing factors such as the amount of reinforcing bars, diameter and spacing of reinforcing bars were analyzed. As a result of the analysis, it was found that the crack width caused by restraint drying shrinkage exceeded the allowable crack width of 0.2 mm for reinforcing bars with a reinforcing bar ratio of 0.01 or less based on the H16 reinforcing bar and a reinforcing bar with a diameter greater than H19 based on the reinforcing bar ratio of 0.01. Finally, based on the results of the crack width review, a method for controlling the crack width of the top flange of the PSCB girder bridge was proposed.
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